board: gateworks: venice: determine dram size at runtime

The SPL does not update the memory node with the dram size from EEPROM
but instead we can use get_ram_size which does a simple memory test
to determine the available RAM. Update PHYS_SDRAM_SIZE to 4GiB as that
is the max used on the Venice boards.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/include/configs/imx8mn_venice.h b/include/configs/imx8mn_venice.h
index e7bfcd7..401084c 100644
--- a/include/configs/imx8mn_venice.h
+++ b/include/configs/imx8mn_venice.h
@@ -80,7 +80,7 @@
 
 /* SDRAM configuration */
 #define PHYS_SDRAM                      0x40000000
-#define PHYS_SDRAM_SIZE			SZ_1G
+#define PHYS_SDRAM_SIZE			SZ_4G
 #define CONFIG_SYS_BOOTM_LEN		SZ_256M
 
 /* UART */